Guard rings are structures that prevent delamination of various layers of the integrated circuit chip and other edge damage which may occur during “dicing” operations, as well as protect the integrated circuit from moisture and ionic contamination. For example, during dicing operations, cracks that extend inwardly from the edges of a chip are halted by the guard ring, which is typically in the form of a metallic ring-like structure positioned between the active region of the chip and the edge of the chip.
More specifically, at a final stage of fabrication, the wafer is cut or diced into individual integrated circuit chips, either by sawing or by scribing and breaking. When diced by sawing or by scribing and breaking, the wafer is subjected to high shear stresses which can cause cracks to form, which extend inwardly from the sawn or scribed and broken edges of each chip. Due to the stresses encountered when dicing the chip or even later during use, cracks can propagate inward from the edges of the chip and eventually reach the active portion of the chip, damaging semiconductor devices within the active portion. The guard ring structure, though, will prevent propagation of the crack into the active region.
For RF devices, the continuous ring of metal can couple to the circuits, creating noise and degrading performance. Hence, it is desirable to have breaks in the guard ring (discontinuous metal) to minimize RF coupling. In such a structure, if the gap in the guard ring is small enough, cracks will not propagate into the active device. However, having a gap in the guard ring is not sufficient to eliminate device coupling, because of the conductivity of the silicon substrate.